Method of making shaped apertures by using focused pattern of ultrahigh frequency sound waves



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F. C. ALEXANDER. JR

Filed Aug. 20, 1965 OF ULTRAHIGH FREQUENCY SOUND WAVES June 24, 1969METHOD OF MAKING SHAPED APERTURES BY USING FOCUSED PATTERN United StatesPatent 'METHOD OF MAKING SHAPED APERTURES BY ABSTRACT OF THE DISCLOSUREA method of making very small non-circular holes in a spinneret forspinning artificial filaments involves focusing a pattern of ultrahighfrequency sound waves on the spinneret while it is immersed in a liquidmedium.

This invention relates to a method of making a shaped aperture or aplurality of shaped apertures in an object and more particularly to amethod of making extremely small non circular apertures or holes. It iscontemplated that the invention will find its greatest utility in makingnon-circular orifices in the face of a spinneret or jet for the spinningof artificial or synthetic filaments.

Generally speaking artificial and synthetic filaments are formed byextruding a solution or a melt through tiny holes or orifices in theface of a spinneret. Uusually, the spinneret is formed of metal, oftenplatinum, but sometimes of other hard material such as a ceramic.Normally the orifices are circular to produce filaments having acircular cross section but not infrequently it is desired to extrude thefilament forming material through orifices which are other thancircular, e.g. square, L-shaped, H-shaped, etc. Circular orifices, evenextremely small ones are of course not too difiicult to make butextremely small orifices of non-circular shape present great difiicultyand while the present invention is useful for making circular orificesthe greatest benefits are derived when making shaped orifices, aperturesor holes which are non-circular.

'It is an object of this invention to provide an improved method ofmaking shaped apertures rapidly and accurately.

A more specific object of the invention is to employ acoustics formaking minute apertures of non-circular shape.

The invention will be described in connection with apparatus forcarrying it out as shown schematically in the accompanying drawingwherein:

FIG. 1 is a side eleva-tional view of the apparatus; and

FIG. 2 is an elevational view of a wave patterning shield constitutingone of the elements of the apparatus.

'In general, the method of the present invention, involves converging orfocusing a pattern of sound waves of ultrahigh frequency and thereforerelatively short wavelength on the object through which the patterned orshape-d aperture is to be made. As indicated above, it is contemplatedthat the aperture will be quite small and that the object in which it isto be made will be a hard material such as used for spinnerets or jetsfor spinning artificial filaments. The spinneret or the like issubmerged in a liquid medium and the elastic sound waves are created inthe medium by any suitable means such as a piezoelectric transducer.These waves, or those portions thereof forming a pattern correspondingto the desired shape of the aperture, are passed through a sonic lenswhich focuses them on the face of the spinneret. The focused andconcentrated waves contain a large amount of energy and where theystrike the spinneret a hole is ice formed by heat and cavitation, aswill presently be ex. plained in more detail.

In the drawing, the spinneret is indicated at 10 and is mounted in abracket 12 within a liquid medium 14 contained in a tank 16. The liquidmedium is preferably gasfree water in which plane longitudinal soundwaves travel with a velocity of about 1460 meters per second, which ishigh with respect to the velocity in air wherein sound waves travel atabout 345 meters per second. Instead of water, other gas-free liquidscapable of transmitting sound waves at a relatively high velocity may beemployed.

Mounted on a bracket 18 within the tank is a piezoelectric transducer 20which is arrange-d to direct planar coherent ultrahigh frequency soundwaves toward the face of spinneret 10. In order to produce awell-defined aperture in the spinneret, the wavelength of the soundwaves in the liquid medium should be not greater than about one-tenth ofthe smallest dimension of the aperture. Since, as mentioned, it iscontemplated that the invention will be employed for making very smallaper-= tures, the output of the transducer must be in the ultrahighfrequency range, preferably above ten million cycles per second. Forexample, in water, sound waves having a frequency of ten thousand cyclesper second and a velocity of 1460 meters per second have a wavelength of14.6 centimeters whereas at a frequency of ten million cycles thewavelength is 0.0146 centimeter and at one hundred million cycles thewavelength is only 0.00146 centimeter. Thus the smaller the orifice, thegreater should be the frequency in order to produce the desired shortwavelength.

Mounted on a bracket 22 in front of transducer 20 is a shield 24 havingtherein a wave patterning opening 26. Opening 26 is correlated inshapewith the shape of the aperture to be made in the spinneret or otherobject but is substantially larger than the aperture. Shield 24 is madeof a material wherein sound waves have a very low velocity and aredissipated quickly whereby efiectively only those waves aligned withopening 26 pass through the shield. The shield may be made of vulcanizedrubber wherein the velocity of sound is only about fiftyfour meters persecond or of wood which is also a good sound barrier or may be laminatedstructure with the face directed toward the transducer reflecting aportion of the wave and a second layer absorbing the unreflectedportion. At this point it should be mentioned that the inside of tank 16is coated with a sound absorbing material such as vulcanized rubberwhereby stray waves are not reflected from the sides of the tank.

Mounted on bracket 28 and located between shield=24 and the spinneret isa converging sonic lens 30 which may be a double concave metal lensformed of :a low energy loss material such as aluminum or magnesium.Lens 30 focuses or images the pattern of waves passing through theshield opening 26 onto the face of the spinneret which is located at thereal focus of the lens whereby the wave energy is concentrated in a muchsmaller area on the spinneret than the area of the shield opening. Thisconcentrated energy heats the spinneret face in a pattern correspondingto opening 26 and at the interface between the spinneret and the liquidmedium the phenomenon known as cavitation takes place. Caviation is arupture of the liquid caused by a sudden increase in velocity of thesound waves as they enter a hard object. The velocity of planarlongitudinal sound waves in platinum is about 2690 meters per second andin a ceramic material may be twice this or more. As mentioned, thevelocity of sound in gas-free water is about 1460 meters per second.This sudden increase in velocity of the sound waves causes tiny vacuumsto form in the liquid and the metal of the spinneret is torn away in thearea of the vacuums. This cavitation. phenomenon is well known as istaken advan-= tage of in ultrasonic cleaning procedures wherein it isthe cavitation phenomenon which removes the unwanted matter but verylittle if any of the material actually forming the body being cleaned isremoved because the sonic waves are not sufiiciently concentrated.However, ac cording to the present invention the sonic wave aredeliberately concentrated by the lens 30 whereby a large amount ofenergy is :focused on the area where the aperture is to be made. Shield24 is not affected by cavitation because it is made of a material inwhich the waves slow down so that vacuums are not formed in the liquidat the interface.

The material of the spinneret in the immediate vicinity of the patternedimage is also affected somewhat so that if it is desired to make anaperture having the exact shape of particular opening 26 -for example,the shape of the opening must be modified, Thus if it is desired toproduce an aperture having sharp corners, the corners of the opening inshield 24 will in practice be slightly concave. It will be apparent thatshield 24 may be provided with a plurality of openings whereby aplurality of apertures may [be formed simultaneously in the spinneret.

Having thus described the invention, what is claimed is:

1. A method of making a shaped aperture in an object formed of a hardmaterial comprising positioning the ob= ject in a gas-free liquidmedium, directing planar coherent ultra high frequency sound wavesthrough the liquid medium toward the object in a pattern correlated withbut substantially larger than the pattern of the shaped aper 4 ture tobe made in the object, and focusing the patterned sound waves by meansof a converging sonic lens on the object located at the real focus ofthe lens.

2. The method set forth in claim 1 wherein the wavelength of the soundwaves in the liquid medium is not greater than about one-tenth of thesmallest dimension of the shaped aperture to be made in the object.

3. The method set forth in claim 1 comprising generating the sound wavesby means of piezoelectric transducer, and providing between thetransducer and the sonic lens a shield which is apertured to permit onlythose waves of the desired pattern to strike the lens,

4. The method set forth in claim 3 wherein the frequency of the soundwaves is at least about ten million cycles per second,

References Cited FOREIGN PATENTS 789,293 1958 Great Britain.

OTHER REFERENCES Schotten and Cook: Mechanical Aids to Metal Cleaning,December 1965, Plating, pp 1280-1284 JACOB H. STEINBERG, PrimaryExaminer.

US. Cl. X.R.,

